Direct catalytic oxidation of methane to formaldehyde: New investigation opportunities provided by an improved flow circulation method

An improved flow circulation reactor with reaction mixture quenching was used to study the direct oxidation of methane to formaldehyde at 600–770°C, a CH₄/O₂ volume ratio of 1: 1 in the starting mixture, and gas mixture flow rates of 0.4–2.0 l/h. It was found that, in the presence of a surface containing SiO₂ (quartz reactor walls, the surface of silica packing materials, or the surface of SiO₂ as a catalyst constituent), the process occurred by a heterogeneous-homogeneous mechanism with chain continuation in the volume of a gas phase. The process was controlled by the size and shape of the free reaction volume, the contact surface area, and the residence time of a mixture in the reaction volume. The introduction of typical oxidation catalysts containing, for example, Pt or V₂O₅ as an active component along with SiO₂ resulted in a decrease in the yield of and selectivity for formaldehyde.     

Osmium liquid-phase catalysts for hydrogenolysis of saturated hydrocarbons and hydrogenation of arenes

Reduction of OsO₄ by molecular hydrogen in alkane (cycloalkane) or benzene (toluene) solution produces small-ligand clusters of osmium of composition Os_1.5–2.5. CH_0–2 with a particle size 10–40 Å and a specific surface area of 34–46 m²/g. Hydrogenation of dry catalyst produces methane. The small-ligand osmium clusters obtained effectively catalyze hydrogenolysis of alkanes and cycloalkanes at 100–150°C and =5 MPa and hydrogenation of benzene at 20°C and =0.1 MPa.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2428–2433, November, 1989.     

Effect of the Porphyrin Structure on the Kinetics of Complex Formation with Zinc Dipyrromethene in Dimethylformamide

The kinetics of complex formation of zinc dipyrromethene with tetraphenylporphyrin, octaethylporphyrin, and 5,15-dipentyl-2,3,7,8,12,13,17,18-octamethylporphine at 368–420 K have been studied. The kinetic parameters (k _app, k _v) of the complex formation processes have been determined. The porphyrin molecules have been optimized by the PM3 quantum-chemical method, and their geometric characteristics have been obtained. The effect of the structure and macrocycle strain of porphyrins on the complex formation rate is discussed.     

Conformational Characteristics of Polyimide Initiator for the Synthesis of Poly(Methylmethacrylate) Grafted Block-Copolymers

Molecular properties of a highly functionalized new polyimide multicenter macroinitiator were studied using viscometry, static and dynamic light scattering, and analytical ultracentrifugation in dilute N,N-dimethylformamide solutions. Exponents of the Mark–Kuhn–Houwink equations were obtained for translational friction and intrinsic viscosity. The studied polyimide is a flexible chain polymer, Kuhn segment length being 2–3 nm.     

Lateral spatial resolution of widened focused transducer array for optoacoustic tomography

Numerical investigation of a point spread function for a optoacoustic transducer array is described. Analysis of the minimal reconstructed dimension for an optoacoustic image of a point source of spherical waves is performed within the proposed approach. The influence of the array geometrical parameters, number of array transducers, and the frequency band of a single transducer on the lateral resolution in the image plane is investigated in detail. It is demonstrated that the lateral resolution obtained with the help of a transducer array in the image plane is determined unambiguously by the frequency band of a transducer, the flare angle of the array, and the transducer width and does not depend on the number of transducers.     

Laser-Ultrasonic Study of Residual Stresses in Pipes Made of Austenitic Steel

Acoustical Physics - The paper discusses an acoustoelastic study of residual stresses and related structural changes in thin-walled austenitic steel pipes. A probing ultrasonic (US) beam is formed...     

Interpolation property for extensions of intuitionistic proof logic

Translated from Matematicheskie Zametki, Vol. 47, No. 5, pp. 88–99, May 1990.